Heat resistant fibrous products containing ceramic fibers and method of making the same



May 21, 1963 TENSILE STRENGTH (lbs) w. P. CRAWLEY 3,090,103 RESISTANTFIBROUS PRODUCTS CONTAINING CERAMIC FIBERS AND METHOD OF MAKING THESAME. Filed Oct. 24, 1957 HEAT ASBESTOS FABRIC 80 (GRADE AAA) CERAMIC-ASBESTOS BLENDED 4O FIBER FABRIC O l I l l l I l J 700 800 900 I000 IIOOI200 I300 I400 I500 TEMPERATURE (F) INVENTOR.

WlLLlAM P. CRAWLEY EATTORNEY 3,090,163 I-EAT RESETANT FTBROUS PRQDUCTSCQNTATN- lNG CEIC FIBERS AND METH'DD OF ENG TI E SAME William P.Crawley, Tonawanda, N.Y., assignor to The Carhorundum Company, NiagaraFalls, N.Y., a corporation of Delaware Filed Oct. 24, 1957, Ser. No.6%,2fi5 Claims. (Cl. 28-78) This invention relates to fibrous productsthat have unusual characteristics of strength and heat resistance.

The ceramic fibers of the aluminum silicates that are now available haveoutstanding heat resistance, but their physical characteristics haverestricted their use. These ceramic fibers are straight anddiscontinuous. They have no natural twist and are brittle and delicate.The fibers are smooth-surfaced, so that there is little or no cohesionbetween the fibers, and because there is no crimp or curl to the fibers,they do not cling together. Moreover, the fibers have low extensibility.Because of these characteristics, these ceramic fibers will not card onconventional machinery, but fall out of the machine.

Fabricated items such as paper, batts, roving, yarn, cord, rope, cloth,and non-woven structures made from various conventional fibers, bothorganic and inorganic, are much more limited in their resistance toheat, according to the heat resistance of the specific fibers used inthese items.

I have found that certain combinations of ceramic fiber of an aluminumsilicate with conventional fibers can be made in the form of intimateblends that can be carded on textile machinery. Fibrous products thatare made from these blends are characterized by unexpected combinationsof strength, heat resistance, and heat dissipation.

Accordingly, one object of this invention is to provide fibrous productsthat have materially increased heat resistance.

A related object of the invention is to provide an intimately blendedfibrous mixture of ceramic fibers of an aluminum silicate and carrierfibers, that can be formed into fibrous products that have substantiallyincreased heat resistance over products formed from the carrier fibersalone, and that have appreciable strength.

Another object of the invention is to provide fibrous products that havegreater strength at high temperatures than fibrous products previouslyavailable.

According to the present invention, fibrous products, includingnon-woven, woven, and knitted products, are made from intimate fiberblends that contain, by weight, between about 10% and about 95% ofceramic fiber, the remainder being a carrier fiber that will permit theceramic fiber to be processed on conventional machinery.

While ceramic fiber that is made from substantially pure aluminumsilicate is the preferred ceramic fiber for use in accordance with theteachings of this invention, it is contemplated that certain otherheat-resistant ceramic fibers could also be used, such as, for example,fibers that contain aluminum silicate together with certain otherinorganic oxides, such as, for example, boron oxide, thoria andzirconia. Ceramic fibers of this type are produced by processes similarto those used for mineral Wool or staple glass fibers, except that themelting point (33% F.) is so high that the heat of an electric arcfurnace is required. The molten mix is formed into fibers by blowingwith steam or air, or by spinning from mechanical rotors. Resistance tohigh temperatures is unexcelled by any fiber with the possible exceptionof pure silica.

Some of the carrier fibers that may be used are acrylic fibers, rayon,cotton, Wool, asbestos, glass, tetrafluoro- 3'90 fl,1 3' Patented May21, 1963 ethylene fibers, polyamide fibers, vinyl fibers, and proteinfibers.

The invention can best be understood by reference to several specificembodiments of the invention that are described in the followingexamples.

The drawing provides a graphical representation of the properties of afabric made according to the embodiment of the invention described inExample I. The drawing comprises a pair of curves, each curve showinggraphically the relationship between tensile strength and heatresistance of the fabric.

EXAMPLE I Fibrous Products Made From Intimate Blends of Ceramic Fiberand Asbestos Fiber An intimate blend of Fiberfrax aluminum silicate longstaple, medium ceramic fiber and carded asbestos fiber, Cassiar gradeAAA, a chrysotile asbestos, was made acconding to the method that isdescribed in the co-pending patent application of John W. Weber, SerialNo. 658,582, filed May 13, 1957, and now Patent 3,012,289. Fiberfrax isa registered trademark of The Carborundum Company, Niagara Falls, NewYork. The long staple grade of Fiberfrax ceramic fiber contains about51.3% silica, about 45.3% alumina, and about 3.4% Zirco-nia. Fiberlength is about 1 /8" average, but varies considerably. The diameters ofthe medium fibers are predominantly in the range 8 to 14 microns, With amean diameter of about 10 microns (about 2 denier). The specific gravityof the fibers is about 2.73 gin/cc. As produced, the fiber contains upto about 65% of nonfibrous solids or shot.

According to the Weber method, the asbestos fibers were carded to form acontinuous web. The Web of asbestos carrier fibers was divided into fourwidths. A mass of the ceramic fibers was opened to make a plurality ofsmall tufts, and these tufts were deposited onto each of the widths ofthe carrier fibers, so that there were a plurality of tufts of ceramicfibers distributed upon each width of the web of carrier fibers. Thewidths of the carrier web, with the tufts of the ceramic fibersdistributed thereon, were superposed to form a pile. The pile was thencarded to form a blended web of carrier fibers and ceramic fibers. Theproportions of asbestos carrier fiber and ceramic fiber were carefullyregulated so that the blended web comprised about 44% by weight ofasbestos fiber and about 56% by Weight ofceramic fiber. Substantially noorganic impurities were present.

The non-fibrous material, or shot, was separated from the ceramic fibersbefore the tufts of ceramic fibers were deposited on the web of asbestoscarrier fibers.

, The blended fiber web was divided into several widths, to form rovingswhich were spun to make yarn. The yarn was woven into a six inch Widetwill weave tape.

Several pieces were cut from the tape for testing purposes. Similar testpieces were obtained from grade AAA asbestos tape of substantially thesame Weight and construction, to provide a standard of comparison. Theseveral test pieces were then placed in ovens, in pairs of one piece ofasbestos tape and one piece of blended fiber tape, at differenttemperatures for 24 hours. Thereafter, the tensile strength, ASTM grabmethod, of the warp was determined for each of these. The results wereplotted, and the curves were reproduced in the drawing.

As the drawing indicates, the asbestos fabric has superior tensilestrength up to a temperature between 1000 F. and 1100" F. Attemperatures above 1000 F., the tensile strength of the fabric made fromthe blend of ceramic fiber and asbestos fiber had a considerablysuperior tensile strength. Even at 1500" F., the fabric from the blendedfiber had appreciable tensile strength.

a For the field of use at temperatures between about 1000 F. and 1500F., therefore, the fabric from the blended fiber is markedly superior toasbestos.

Representative points on the curves are as follows:

TABLE I Tensile strength, lbs. Time, hrs. Temp., F.

Asbestos Cloth from cloth blended Unheated tapes RJI. 159v 85. 0 24 1,000 55.0 35. 0 24. 1, 150 13. 24. 1, 300 2.0 20.0 24 1,500 10. 5

The entries under the temperature column in Table I indicate thetemperature at which the respective samples were held for 24 hours,before their tensile strength was determined. The superiority of theasbestos fabric is evident until temperatures on the order of about 1000are reached, but above 1100 F., the cloth from the blended fiber ismarkedly superior in strength, appearance, and hand.

One sample of the asbestos tape, and one sample of the tape made fromthe blended fiber, were held in a furnace for 24 hours at 1000" F. Theweights of these samples were recorded before and after furnacing. Theresults are presented in Table H, below.

TABLE II Weight, in grams Sample Before After Percent iurnacingiurnacing loss Blended sample 36. 56 35. 67 2. 4 Asbestos tape 26. 0821. 58 17. 2

TABLE III Load in lbs. Percent of the Temp, F. at the break originalpoint; strength retained a 1 Completely melted.

In another test, two one-inch wide ravelled strips of the tape wereloaded with Weights, one with three pounds (approximately 5% of breakingload at room temperature), and the other with nine pounds (approximately15% of breaking load at room temperature). The two strips were thenheated gradually in an oven. After 95 minutes of heating, and at atemperature of 2310" F., the strip with the nine pound load failed.After 110 minutes of heating, and at 2360 F., the strip with the threepound load failed.

On the basis of the foregoing data, it is apparent that temperatures inthe neighborhood of 2350 F. are critical with regard to the loadbreaking properties of this particular tape. At temperatures up to about2000 F., the material exhibits reasonably good resistance to static loadstresses, and if vibrations or shearing action are not prescut, the tapeundoubtedly would resist destruction under static load for aconsiderable period of time.

bestos to ceramic fiber appear timate blends for products for omy. Inthe range 1400" F. to 1800 F., blends of 40% to 60% asbestos with thebalance ceramic fiber would be most practical. In the range 1-800 F. to2300 F., blends of 10% to 40% asbestos with ceramic fiber would be mostpractical. Typical applications for fibrous products made from intimateblends of asbestos fiber and ceramic fiber include heat barriers of alltypes, such as for example, furnace curtains, lagging, fireshields, firescreens, heat insulating materials, and the like. Felted products madefrom these intimate blends of fibers are useful for high temperature gasfiltration, as Well as for many other purposes.

EXAMPLE II Blends 0 Ceramic Fiber and Acrylic Fiber Fibrous productsmade from cotton, nylon, acrylic fiber, and cellulose acetate fiberwould have a much more broad field of use, if the temperature resistancewere increased even moderately. For example, in the filtration field,the manufacture of collector bags consumes a large amount of specialcloth annually. For example, filament glass cloth treated with asilicone resin is used extensively in the manufacture of dust collectorbags for carbon black collection. This cloth is resistant to continuoustemperatures of 400 F., and has a useful life of between 12 and 18months. Considerable processing economies would be available if a fabricwere available that could be used to make these bags, and that couldWithstand temperatures in the range of 500 F. up to 550 F.

According to the present invention, such fabrics can readily be preparedby making cloth from intimate fiber blends that have predeterminedproportions of acrylic carrier fiber and ceramic fiber of an aluminumsilicate.

A blend can be prepared of 25% by weight Fiberfrax long staple, mediumceramic fiber and 75% by weight Orion acrylic fiber. Orlon" is aregistered trademark of the E. I. du Pont de Nemours Co., Inc.,Wilmington, Delaware, for an acrylic fiber made from polymerizedacrylonitrile. The intimate blend of fibers can be spun to form a yarn.The yarn has good strength and unusual heat resistance up to around 300'F. It can be woven to form insulating cloth, filter elements, gaskets,and packings, of unusual heat resistance.

Woven products made from this intimate fiber blend can be heat treatedat temperatures above about 320 F., and preferably in the range of 400F.to 600 F., in circulating air or other oxidizing atmosphere, forsuflicient time to permit the acrylic fiber to undergo a change incharacter to a non-flammable state. An exothermic reaction takes placeunder these conditions, and it is believed that the acrylic fiber isconverted to linear, heterocyclic form. The fibrous product must be heldabove 320 F., in contact with air, for sufiicient time to permit thereaction to be completed, otherwise, the product will be flammable.Ordinarily, for woven fabrics, periods from one-half hour to three hoursare sufficient. When the acrylic fiber has been heat treated in thismanner, as described in detail in a copending patent application SerialNo. 692,206, filed October 24, 1957, fireproof fabrics are obtained thathave excellent heat resistance. Thus, the yarn above can be woven toform a fabric weighing ten oz./sq. yd. When this fabric is heat treatedas described, it can be used for filtration bags and for active filterelements, and in other applications, at continuous temperatures up toabout 600 F. Even higher service temperatures are permissible when thefiber blend contains a greater proportion of ceramic fiber.

EXAMPLE III Fibrous Products Made F ram. Blends of Ceramic Fiber andOrganic Fiber Several intimate blends containing 70 parts by weight ofFiberfrax long staple medium ceramic fiber and 30 parts by weight ofcarrier fiber were prepared. The carrier fibers were as follows:

Fiber: Description Cotton 1%" staple, from picker lap. Nylon 3 denier,garnett stock. Dynel acrylic fiber- 3 denier, 1 /2" staple. Celluloseacetate 3 denier, 1 /2" staple.

Dynel is a registered trademark of Union Carbide Corporation for itsacrylic fiber, made from a copolymer of vinyl chloride andacrylonitrile.

The fiber blends were made by hand picking the component fibers andmaking a sandwich-type mix. The mix was then broken down vertically andre-sandwiched. This was repeated for a total of three blendings. Thestock was then hand fed to a single cylinder card equipped with ringdoffers and rub aprons.

An examination of the blended webs from the card indicated that theblended Webs that contained cotton and nylon had a fair degree of fiberblending, and that the acrylic fiber and cellulose acetate fiber blendshad a better degree of fiber blending.

All of these blended webs were characterized by enhanced heat resistanceand good yarn-making properties. Fibrous products made from the blendedwebs serve admirably for high temperature packing and for thermalinsulation.

Since roping and yarn strength depend primarily upon the carrier fiber,good fiber blending is necessary for making satisfactory roping andyarn. Since the blended webs containing the acrylic fiber and thecellulose acetate were characterized by good fiber blending, these webswere selected for further processing, and were formed into yarn on awoolen spinning frame. The resulting yarns from both types of fiberblends were satisfactory, although there were indications that betterresults would be obtained from mechanically blended fibers. Drafts ashigh as 1.25 were used successfully in making the yarns.

All four blended webs, that is, the hand-picked, carded, blends ofceramic fiber and cotton, nylon, acrylic fiber, and cellulose acetate,respectively, were also hand-twisted to form ropings or yarns. Thetwisted ropings were suspended vertically, and a small weight was thenattached to each at its lower end. The fiame of a match was rought intocontact with each strand. The carrier fibers of nylon and cotton burned,leaving parted strands indicating no residual strength. The acrylicfiber and cellulose acetate fiber blacknened and shrank, but theresidues apparently provided a bonding action which held the unburnedceramic fibers together, since some yarn strength remained.

EXAMPLE IV Blended Rayon Fiber and Ceramic Fiber Yarn was made bycarding and spinning a blend of 80 parts by weight of rayon and 20 partsby weight of Fiberfrax long staple, medium ceramic fiber. The rayon was1.5 denier, 1 /2 staple fiber. The ceramic fiber had a mean diameter ofabout 4- microns, with a minimum of about 2 microns, and a maximum ofabout 40 microns (average, about 055 denier). Staple length of theceramic fiber averaged about 1%", with some variation between individualfiber lengths.

The fibers were carded and spun to form an eight oz./ sq. yd. cloth thathad a yarn count of /2 warp and filling. This cloth had excellent heatresistance and made an excellent material for use as press clothmaterial.

Another blended web was prepared that contained 15% by weight of ceramicfiber and by weight of rayon. This blended web was formed into yarn thatwas spun to form a light weight fabric that had excellent heatresistance. This fabric had characteristics that made it a superiormaterial for use for ironing board covers, and for similar applicationswhere enhanced resistance to heat and scorching is important.

Intimate blends of rayon fibers and ceramic fibers of an aluminumslicate have excellent textile properties, particularly where the rayonfibers comprise 70% to 85% by weight of the blend. Fibrous products fromsuch blends have enhanced heat resistance with very little sacrifice inhand, appearance, and strength.

The foregoing examples illustrate certain specific embodiments of theinvention. It should be appreciated that many other combinations ofcarrier fiber with the ceramic fiber are possible, and are contemplatedwithin the scope of this invention. For example, the asbestosfiber-ceramic fiber blends described in Example I can be modified, forspecial purposes, by incorporating still other fibers in the intimateblend.

Generally, the ceramic fibers range in size from about 2 to about 20microns, although fibers with diameters up to about 80 microns can beused successfully. In general, the ceramic fiber constitutes at leastabout 10%, and preferably at least 15%, by weight of the fiber blend, toachieve a substantial upgrading of heat resistance. The maximumproportion of ceramic fiber that can be employed, under the bestpossible conditions, with the most suitable machinery now availableapproaches 95% by weight of the blend. For most high temperatureapplications, however, the preferred amount of ceramic fiber in a blendof fibers is on the order of 80% to that is, about 10% to 20% by Weightof the blend comprises carrier fibers.

The ceramic fibers that can be used, in accordance with the teachings ofthis invention, contain a major proportion of aluminum silicate,together with small amounts of boric oxide, zirconia, or other fluxes.Ceramic fibers of this type are readily available in a variety ofdeniers. For good processing characteristics, the longer fibers, oflarge diameter, are preferred. The fiber diameters preferably should bepredominantly in the range between 2 and 20 microns.

While certain carrier fibers have been described above in relation tospecific embodiments of the invention, it will be understood that manysuitable carrier fibers can be used. Rayon is a highly desirable carrierfiber for many purposes where resistance to extremely high temperaturesis not required, because rayon is a precision fiber. The acrylic fibersand other synthetics are also precision fibers, so that processing canbe facilitated by selecting, for blending with the ceramic fiber, acarrier fiber that will have, consistently, optimum carriercharacteristics. However, the natural fibers, such as, for example, wooland cotton, can also be used.

Some of the organic carrier fibers that can be employed tend to shrinkat elevated temperatures. In the fibrous products p epared according tothis invention, however, fiber shrinkage upon exposure to heat is oftennot a serious problem. This is particularly true where the ceramic fiberconstitutes the major proportion of the fiber blend.

In any woven fibrous product made according to the teachings of thisinvention, the fibers are bound together by twist and fiber to fibercohesion, and therefore, tensile strength is not substantial at hightemperatures. Higher tensile strength can be obtained by insertedmaterial such as alloy wire. Under many conditions, a glass filamentyarn, or an asbestos yarn insert, provide adequate strength, but forextremely high temperature applications where the temperaturelimitations of these inserts are exceeded, wire is necessary.Nickel-chrome alloy wire and stainless steel Wire are good insert Wiresfor high temperature applications.

The fibrous products of this invention can be formed readily insubstantially any desired fabricated form. For example, herringboneWeave cloth, twill Weave tape, tubular Woven fabric with a stainlesssteel Wire insert, paper, batts, blankets, roving, yarn, cord, rope, andthe like, can be produced readily.

The ceramic fibers provide heat-resistant and heatdifiusing members inthe products, and thus upgrade the heat resistance. The ceramic fiberoffers particular advantages in products where previous failures hadbeen caused by a surface or localized heat condition.

' Specific fibrous products that may be improved, ac cording to theteachings of this invention, include lami nating paper for hightemperature applications, laundry cloths, and many other textiles forhigh temperature applications. Many other specific fibrous products arementioned above.

While the invention has been described in connection with specificembodiments thereof, it will be understood that it is capable of furthermodifications, and this application is intended to cover any variations,uses, or adaptations of the invention following, in general, theprinciples of the invention and including such departures from thepresent disclosure as come Within known or customary practice in the artto which the invention pertains and as may be applied to the essentialfeatures herein before set forth, and as fall within the scope of theinvention or the limits of the appended claims.

I claim:

1. A blended, fibrous product characterized by a high degree of strengthretention at temperatures between 1000 F. and 2000 F. and consistingessentially of an intimate carded mixture of staple, inorganic,siliceous, ceramic fibers containing a major proportion of aluminumsilicate andstaple carrier fibers consisting essentially ofasbestos,'said ceramic fiber constituting from about 10% to about 90% byweight of said product.

2. A strong, heat-resistant fabric, adapted for service at temperaturesin the range from about 1000 F. to about 2300" F. which involvesmaintenance of substantial tensile strength, said fabric being wovenfrom yarns consisting essentially of carded and spun, intimate mixturesof staples, inorganic, siliceous, ceramic fibers containing amajorproportion of aluminum silicate and staple carrier fibers consistingessentially of asbestos, said ceramic fibers constituting from about 10%to about 90% by weight of said fabric,

3. A strong, heat-resistant fabric, adapted for service 'at temperaturesin the range from about 1000" F. to about 1400 F. which involvesmaintenance of substantial tensile strength, said fabric being wovenfrom yarns consisting essentially of carded and spun, intimate mixturesof staple, inorganic, siliceous, ceramic fibers containing a majorproportion of aluminum silicate and staple carrier fibers consistingessentially of asbestos, said ceramic fibers constituting from about 10%to about 40% by weight of said fabric.

4. A strong, heat-resistant fabric, adapted for service at temperaturesin the range from about 1400 F. to about 1800" F. which involvesmaintenance of substantial tensile strength, said fabric being wovenfrom yarns consisting essentially of carded and spun, intimate mixturesof staple, inorganic, siliceous, ceramic fibers containing a majorproportion of aluminum silicate and staple carrier fibers consistingessentially of asbestos, said ceramic fibers constituting from about 40%to about by Weight of said fabric.

5. A strong, heat-resistant fabric, adapted for service at temperaturesin the range from about 1800 F. to about 2300 F. which involvesmaintenance of substantial tensile strength, said fabric being wovenfrom yarns consisting essentially of carded and spun, intimate mixturesof staple, inorganic, siliceous, ceramic fibers containing a majorproportion of aluminum silicate and staple carrier fibers consistingessentially of asbestos, said ceramic fibers constituting from about 60%to about by weight of said fabric.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Modern Textiles, September 1957, page 61.

1. A BLENDED, FIBROUS PRODUCT CHARACTERIZED BY A HIGH DEGREE OF STRENGTHRETENTION AT TEMPERATURES BETWEEN 1000* F. AND 2000* F. AND CONSISTINGESSENTIALLY OF AN INTIMATE CARDED MIXTURE OF STAPLE, INORGANIC,SILICENOUS,